1. Field of the Invention
The present invention relates to an optical module used for optical communication and the like.
2. Related Art
Optical parts which have functions such as optical branching, optical switching, wavelength multiplexing/de-multiplexing and the like has a popularity in the field of optical communication. Even though there are various kinds of optical parts, especially a planar lightwave circuit (PLC) chip which has a waveguide forming region including an optical waveguide circuit on a substrate is in practical use because of its potential possibility of integration and mass production.
A substrate for a planar lightwave circuit chip is, in general, made of silicon, quartz or the like. A waveguide forming region made on the substrate is, in general, made of materials including quartz or the like.
FIG. 8 and FIG. 9 illustrate an example of the planar lightwave circuit chip. A planar lightwave circuit chip 1 comprises a waveguide forming region 10 with an optical waveguide circuit on a substrate 11 made of silicon.
FIG. 8 illustrates a sample of the planar lightwave circuit chip which makes a 1×8 optical waveguide circuit as a circuit for an optical waveguide. FIG. 9 illustrates a sample of the planar lightwave circuit chip which makes a circuit of an arrayed waveguide grating (AWG) as a circuit for an optical waveguide. The arrayed waveguide grating is used for wavelength multiplexing communication, and various kinds of circuits using the arrayed waveguide grating are proposed.
As shown in FIG. 8, the 1×8 optical waveguide circuit has one optical input waveguide 12 and eight optical output waveguides 16, and a plurality of branching parts 37 between the optical input waveguide 12 and the optical output waveguide 16.
As shown in FIG. 9, the circuit of the arrayed waveguide grating has at least one optical input waveguide 12, a first slab waveguide 13 connected to an output side of the optical input waveguide 12, an arrayed waveguide 14 connected to an output side of the first slab waveguide 13, a second slab waveguide 15 connected to an output side of the arrayed waveguide 14A and plurality of optical output waveguides 16 insatlled in parallel and connected to an output side of the second slab waveguide 15.
The arrayed waveguide 14 transmits a light beam outputted from the first slab waveguide 13, and it includes a plurality of channel waveguides 14A installed in parallel. Length of the adjacent channel waveguides 14A is different by the predetermined length (ΔL).
In general, a lot of (for example, one hundred) channel waveguides 14A composing the arrayed waveguide 14Are installed. For example, the optical output waveguides 16 with number corresponding to the number of optical signals with different wavelength multiplexed or de-multiplexed by the arrayed waveguide grating are installed. In FIG. 9, all of the channel waveguide 14A and optical output waveguide 16 are not illustrated so as to simplify the drawing.
In the circuit of the arrayed waveguide grating, as shown in FIG. 9, when a wavelength multiplexed light beam is inputted into one optical input waveguide 12, the wavelength multiplexed light beam is inputted into the first slab wavelength 13 through the optical input waveguide 12, and inputted into the arrayed waveguide 14 with spreading out by the diffraction effect and transmitted in the arrayed waveguide 14.
The light beam transmitted to the arrayed waveguide 14 reaches the second slab waveguide 15, and then is collected to the optical output wavguide 16 and outputted from the optical output wavguide 16. However, there is difference of phase in each light beam transmitted in each channel waveguide 14A of the arrayed waveguide 14 because length of each channel waveguide 14A is different each other. The wavefront of collected light beam is tilted corresponding to the difference of phase, and position to collect the light beams is determined according to the tilted angle. Therefore light beams with different wavelength can be outputted from the different optical output waveguide 16.
For example, as shown in FIG. 10, the planar lightwave circuit chip 1 which has the circuit of the above-mentioned arrayed waveguide grating and the circuit of the optical branching waveguide is contained in a package 2 and used as an optical module. An optical module means an item where optical fibers are connected to the planar lightwave circuit chip and the flat optical wavelength chip is contained in the package.
FIG. 10A is a perspective view of the optical module, and FIG. 10B is a perspective view from the top of the optical module, and FIG. 10C is a sectional view A—A in FIG. 10B.
The planar lightwave circuit chip 1 which has planar lightwave circuit circuit such as arrayed waveguide grating and the like has, in general, a small camber because of difference of coefficient of linear thermal expansion between silicon which composes the substrate 11 and quartz which composes the waveguide forming region 10.
For example, as shown in FIG. 11, the planar lightwave circuit chip 1 has a camber with a convexity on the waveguide forming region 10 side. The camber as shown in FIG. 11 is exaggerated so as to understand the explanation easily.